Studies in the Gait Laboratory of the Department of Rehabilitation Medicine have focused on the control of balance. simultaneous measurement of body angles, foot-floor forces and multiple electromyograms (EMGs) are possible. When standing subjects make rapid are movements, postural muscle activity precedes activity in arm muscles. Biomechanical analysis shows that the role of this activity is to prevent significant displacement of the center of gravity during the movement and to prevent all but the most minor alterations in angles of the body. We have initiated similar studies in patients with parkinson's disease and cerebellar disturbances. Using 0-15 labelled water as a marker for cerebral blood flow in PET studies, we have look for changes in the motor cortex with simple hand movements. We have found an increase in the cerebral blood flow contralateral to voluntary wrist flexion/extention in the motor cortex and supplementary motor cortex. In patients with Parkinson's Disease there was an added delay in initiating movement when the patients were required to remember the location of a targeted movement. Patients with cerebellar hemispheric atrophy failed to improve the performance of sequential movements done with normal vision, whereas patients with olivo- ponto-cerebellar atrophy only showed a deficit in performance of sequential movements guided with mirror-vision. In normal subjects, triggered muscle responses produced by stopping voluntary movements were different from muscle responses occurring during voluntary movement only when the movements were stopped in the beginning of the movement. In evoked potential studies, we determined that the adequate interelectrode distances for mapping somatosensory evoked potentials (SEP) is approximately 2.3-3 cm. By using this spatial sampling, we could differentiate maps of SEP obtained to stimulation of different fingers, median and ulnar nerve at the wrist or a the elbow, and cutaneous stimulation of the skin overlying forearm, arm, and shoulder. It was also possible to differentiate sensory maps obtained to stimulation of distal and proximal areas of the leg.